Gas Engine FAQ

[al_voisine]

Originally Posted by Pinecone

One thing that may help your understanding of leaning is that the engine burns air and fuel by WEIGHT. But we meter by VOLUME.

So the engine pulls in X cubic units of air, and the carb supplied Y cubic units of fuel.

As the air density goes down (due to temp increase, humidity increase, or pressure decrease) you get less WEIGHT of air into the engine. And the air density varies more with temperature than the fuel denstiy does. So you have to also decrease the weight of fuel being supplied, so you decrease the volume by leaning the needles.

And the converse when the air density increases (temperature decrease, humidity decrease, pressure increase).

And humidity and pressure do not change fuel density, but do change air density.

Terry - Thanks for that. It actually made it in amongst the grey cells.

AL

[jockstrap]

Originally Posted by pnchurch

Question is, how do you guys kill the engine?! To date I have done this using the kill switch, now this option is gone, I can't figure out what to adjust to turn the engine off from the remote.

Yes - I use the same method as Doug...

I adjust my throttle low endpoint so approx center trim on throttle (and full low stick) gives me idle.
My Hold switch set at about the same amount.

To kill the engine I simply apply full trim down on throttle. Then restor it to middle for next startup.

[AtTheCross]

i use the kill throttle feature on the dx8, mapped to the trainer button

[Azalin]

Originally Posted by AtTheCross

i use the kill throttle feature on the dx8, mapped to the trainer button

How did you managed to map it to the trainer button?

[AtTheCross]

from main menu>throttle Cut>change SW to 'Trainer' on the Pos: just keep changing the number till the throttle turns the motor off, mine is -7%

[Azalin]

Thanks. It seems it is not possible in JR9503 radios.

[pnchurch]

Thanks all. Finally managed to get the engine to shutdown from the remote. Much appreciated.

[rockinar]

For those of you who are confused on how to measure ratios, here's a solution.

It's called Ratio Rite.

It's a cup you pour the oil in and it has lines on it to show yo how much oil for various ratios for everything between 2oz and 2.5 gallons. That way you can pre mix small enough fuel for what you are only going to be using that day. No need to mix a gallon at a time.


http://www.amazon.com/Unknown-RATIO-.../dp/B0045L9FJM


You can get them at Amazon, or any motorcycle shop that sells dirt bikes, jet skis and such will most likely have them too.

[Seasick78]

Originally Posted by rockinar

For those of you who are confused on how to measure ratios, here's a solution.

It's called Ratio Rite.

It's a cup you pour the oil in and it has lines on it to show yo how much oil for various ratios for everything between 2oz and 2.5 gallons. That way you can pre mix small enough fuel for what you are only going to be using that day. No need to mix a gallon at a time.


http://www.amazon.com/Unknown-RATIO-.../dp/B0045L9FJM


You can get them at Amazon, or any motorcycle shop that sells dirt bikes, jet skis and such will most likely have them too.

+1 - no guess work with Ratio-Rite!


-- Josh

[conntaxman]

Has anyone saw this gasser and motors.
http://www.espritmodel.com/century-r...elicopter.aspx
RJX Black CF Xtreme Gasser 26cc helicopter kit carbon tail blade
http://www.ebay.com/itm/RJX-Xtreme-G...item4d01f95c01
and this/these motors
http://www.aliexpress.com/item/crrc-...278269439.html
Im thinking of getting one. Need some advice.
tks
John

[xfc3dcd]

I had never taken the time to read this thread before and had one comment regarding Coleman fuel's octane varying. After four years of using it, I have never had to make significant needle valve changes from one gallon to the next. It runs much smoother in my engines than 87 octane at the cost of slightly lower rpm.

[rcnut]

I maiden my Whiplash this last Sunday. Only got one tank through it. I ran it out of gas and performed a forced landing. I had a much lower head speed than what I'm used to, so I bounced it in and the heli rolled / hopped over on its side, then slid to a stop! Damage was extremely minimal, 2 servo arms broke, plus a lot of scratches...not bad though.

Anyhow, I set the needles per the instructions (TRM270TT motor), 1-3/8 on the low and 1-1/2 on the high, plus a 1/16 on both just to make sure it was rich. The motor started right up and was idling nicely.

Then yesteday I took my Whiplash out foe 3 more flights. The motor was running rich with a low RPM (maybe around 1550-1600) for the first flight of the day, the heli had a small wobble, due to a lower head speed. But on the 2nd flight the motor started running better, and it was flying smoother! I filled the tank for the third flight and re-adjust the throttle curve for a lower rpm, trying to keep it down. Even after adjusting the throttle curve, the motor bounced back just a little. It's liking the higher head speed and it fly's better!

I have a total of 4 flights on it now and I'm not sure if I should adjust the needles a bit more rich, or just leave them alone for the time being.

Thanks!

[fourbie]

I'm a bit old school and tended to prefer to hover at half stick with nitro. What would you suggest is the best throttle curve for my gasser for that please?

[helivader]

Originally Posted by Azalin

My g270rc wont hower with the curve blow.
After i set the curve 0, 25, 50, 75, 100 it's like normal.

It looks like the carb response goes linear. Any ideas?

My OS GT15HZ on TREX 700N behaves exact like that. It does not even get up to 1800rpm at max throttle. The best it can do is ~ 1700rpm.

How did you overcome this problem ? Would appreciate your feedback.
I spent many weeks try to sort out this problem but still can't. I think I might get rid of it and get a nitro engine for good.

[goodhunting]

I realize that this is an ancient thread but I thought I'd best post in here....

Fairly new to gassers but not to RC helicopters... have a Vario gasser with Zenoah 23cc engine. I fitted the electric start on it and been hovering and gently adjusting to a heavy gasser. I fly scale so no fast moves or 3D... at least not intentionally...

I use a Vbar blue with Pro software (actually running Scale software setup) and I use the Vbar internal governor and Jr RPM sensor with a magnet fitted on the main gear and not on the engine shroud..
The gear ratio is 9,09:1 and I am trying to determine how to calculate the RPM to set the desired headspeed...

Vario reccomends the max headspeed at 1270 RPM. Now I have no clue how much RPM the Zenoah engine puts out in order to calculate the final RPM at the head. Can anyone help me out with this?

Klem

[jharkin]

Originally Posted by goodhunting

I realize that this is an ancient thread but I thought I'd best post in here....

Fairly new to gassers but not to RC helicopters... have a Vario gasser with Zenoah 23cc engine. I fitted the electric start on it and been hovering and gently adjusting to a heavy gasser. I fly scale so no fast moves or 3D... at least not intentionally...

I use a Vbar blue with Pro software (actually running Scale software setup) and I use the Vbar internal governor and Jr RPM sensor with a magnet fitted on the main gear and not on the engine shroud..
The gear ratio is 9,09:1 and I am trying to determine how to calculate the RPM to set the desired headspeed...

Vario reccomends the max headspeed at 1270 RPM. Now I have no clue how much RPM the Zenoah engine puts out in order to calculate the final RPM at the head. Can anyone help me out with this?

Klem

Sure, this isn't to difficult. Since you have the governor sensor on the maingear its reading head rpm directly. So you would go into the governor setup, and if it has a seting for gear ratio, set that to "1:1" or "1" and then just set your desired speed as 1270.

Since your main gear ratio is 9.09, at that headspeed your engine rpm will be 1270 x 9.09 = 11,544 rpm.


If you run into other questions on setup you might want to start a dedicated thread. I dont own a vario but other here do and can answer questions. We also have a bunch of guys who use vbar and can help on settings.

[rbort]

I've flown those helis in the past and found the best head speed with the 9.09 gear ratio is 1400. In the 1200's its just too slow. The lowest I would run would be 1320. Max would be 1450. Try the governer set to 1350, 1400, and 1450 and see how those speeds feel.

Best regards.

-=>Raja.

[goodhunting]

Thanks for the replies. So if I set the gear ratio to 1:1 I should be OK... and that meas that Vbar will pick up the point and set the head RPM at whatever I set this..?
Maybe I should post this to Vbar section...

Raja... the manual states 1270... that's why I wanted to hunt down this number... Just by the feel of it I know I was waay faster than that when I flew it so far... and I though that 1400 RPM would be better... this is what I have at my electrics for 4 blade head and I know it works... with a 2 blade head I go faster than that... (1600 ish range)...

for some reason I wanted to approach this as I do with electrics... there I know the max engine RPM (Kv of motor) and I do the math to get me to the desired head RPM... so I guess here the engine has a larger span of RPM it can run?

Klem

[rbort]

The engine is going to run best in the 12k range. In normal mode you're not looking for engine performance but the slowest speed the helicopter feels comfortable with. I've flown your helicopter at 1250, 1270, 1300, all the way to 1480. In my opinion I felt that 1320 is the slowest I wanted to go. You can try all different speed in that range, heck start from 1250 and work up and see what feels good to you.

My impression, 1400 was ideal and the best all around speed. 1480 is the max you could go, the heli felt like it started to rev too much after this rpm.

-=>Raja.

[goodhunting]

Ok. I’ll five it a try today and see what happens...

Klem


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